The present invention relates generally to x-ray tubes and more particularly to x-ray tubes for volume computed tomography (CT) protocols.
A volume CT scan is typically generated by rotating an x-ray tube around an examination area while a subject is moved through the examination area. Cardiac screening, lung cancer evaluation and other volume CT protocols require larger coverage areas. Current technology requires lengthy scan times and requires elongated breath hold times from a subject in order to image an entire region of interest.
Several techniques have been applied in order to increase coverage of the x-ray anode, thereby reducing scan time and improving the subject's comfort level. For example, in one technique, x-rays are collimated from a single focal spot into two or more planes of radiation. However, the planes are not parallel and only a small number of planes are generated. Therefore, several revolutions are needed to cover any significant volume.
Another approach moves the x-ray tube in a circular path, with the focal spot of x-rays reciprocating at high speed. The focal spot of x-rays moves on a plane of ribbon. However, the focal spot is removed from the target, meaning it is spaced a distance from the target. Further, the focal spot is too big. The result of these two drawbacks is a fuzzy image. Yet another approach uses two targets and a single source to produce an x-ray fan beam having a width of 88 mm. While the width is larger than conventional beam widths, which are typically on the order of 60 mm, the quality of the image becomes compromised due to distortion of the image.
To avoid image distortion and obtain a high quality image, it is necessary to maintain the x-ray beam as flat as possible. In the approach that uses an 88 mm width, a true flat slice is not taken. The scan helix becomes flattened and upon reconstruction of the image using an x-ray that is not flat, the image appears distorted. Other approaches include a larger diameter anode and a plurality of x-ray tubes within a common gantry.
There is a need for an x-ray anode that provides a thick fan beam for improved coverage at the detector resulting in shorter scan times for volume CT applications without compromising the quality of the image.